By area, the Kaipara Harbour is one of the largest harbours in the world. It covers 947 square kilometres (366 sq mi) at high tide, with 409 square kilometres (158 sq mi) exposed as mudflats and sandflats at low tide.[1][2][3]

According to Māori tradition, the name Kaipara had its origins back in the 15th century when the Arawa chief, Kahumatamomoe, travelled to the Kaipara to visit his nephew at Pouto. At a feast, he was so impressed with the cooked root of the para fern, that he gave the name Kai-para to the district. "Kai" means food in the Māori language.[4]

The harbour extends for some 60 kilometres (37 mi) from north to south. Several large arms extend into the interior of the peninsula at the northeast of the harbour, one of them ending near the town of Maungaturoto, only ten kilometres (6 mi) from the Pacific Ocean coast. The harbour has extensive catchments feeding five rivers and over a hundred streams, and includes large estuaries formed by the Wairoa, Otamatea, Oruawharo, Tauhoa (Channel) and Kaipara. A number of small islands off the shoreline are connected to the mainland by mudflats at low tide.

The Kaipara Harbour is broad and mostly shallow, as it is formed from a system of drowned river valleys.[5] The harbour shoreline is convoluted by the entry of many rivers and streams, and is about 800 kilometres (500 mi) long,[6] being the drainage catchment for about 640,000 ha of land.[7]

The harbour entrance is a channel to the Tasman Sea. It narrows to a width of 6 kilometres (3.7 mi),[8] and is over 50 metres (160 ft) deep in parts. On average, Kaipara tides rise and fall 2.10 metres (6.9 ft). Spring tidal flows reach 9 km/h (5 knots) in the entrance channel and move 1,990 million cubic metres per tidal movement or 7,960 million cubic metres daily.[9]

The harbour head is a hostile place. Big waves from the Tasman Sea break over large sandbanks about five metres below the surface, two to five kilometres from the shore. The sand in these sandbanks comes mainly from the Waikato River. Sand discharged from this river is transported northward by the prevailing coastal currents. Some of this sand is carried into the Kaipara harbour entrance, but mostly cycles out again and then continues moving northwards along the west coast. The southern sandbanks at the entrance are constantly accumulating and releasing this sand.[9]

These treacherous sandbanks shift and change position, and are known locally as the graveyard. The graveyard is responsible for more shipwrecks than any other place in New Zealand, and has claimed at least 43 vessels—some say as many as 110.[10][11]

In Māori mythology, the ocean-going canoeMāhuhu voyaged from Hawaiki to New Zealand and overturned on the northern side of the entrance. It was commanded by the chief Rongomai, who drowned. His body was eaten by araara (white trevally), and his descendants to this day will not eat that type of fish.[4][12] The first European shipwreck was the Aurora, a 550-ton barque, in 1840,[13] and the most recent was the yacht Aosky in 1994.[14] Today, the remains of wrecks still become visible under certain tidal and sand conditions.

For this reason, the Kaipara is rarely used today for shipping, and no large settlements lie close to its shores, although many small communities lie along its coastline.

Land habitats adjacent to the harbour support some rare botanical species, including native orchids, the king fern, and the endangered kaka beak.[15]

In particular, Papakanui Spit on the south head of the harbour entrance, a mobile sandspit, is important as a breeding and roosting area for the New Zealand dotterel and the fairy tern. It also has areas of pingao.[18] The spit was an important habitat for the Caspian tern. The birds have moved to other parts of Kaipara Harbour, possibly due to human disturbance. An air weapons range used by the New Zealand Defence Force is a short distance south of the spit.[19][20]

Māori settlements and marae have been scattered around the harbour margins for hundreds of years. The waterways of the Kaipara provided, and still provide, Māori with resources and a ready means of moving between marae.[21]

Today most marae are associated with the Ngāti Whātua sub-tribes, Te Taoū and Te Uri-o-Hau.[21] These sub-tribes both descend from the chief Haumoewhārangi who settled on the north end of the Kaipara entrance at Poutō. He was killed in an argument about kūmara (sweet potatoes). His widow Waihekeao developed a partnership with a Tainui warrior chief, Kāwharu. Kāwharu led several destructive campaigns around Kaipara. Eventually the descendants of Waihekeao and Haumoewhārangi came to control the Kaipara Harbour. Te Uri-o-Hau was founded by Hakiputatōmuri, and controlled the northern part of Kaipara Harbour. Te Taoū was founded by Mawake, and controlled the south.[22]

Dargaville statue commemorating the gumdiggers of early European settlement times.

In 1839, European settlers began arriving in the Kaipara to fell and mill kauri trees and build boats for local requirements.[21] Despite the perilous bar at the harbour entrance, the Kaipara became a busy timber port from the 1860s, shipping thousands of tonnes of kauri timber and gum.[23]

The Wairoa is the main river feeding the Kaipara from the north. Thirty kilometres upstream, the town of Dargaville was established. The stretch of water to Dargaville is broad and straight and provides an easy to navigate route into what were then kauri forests in the interior. Dargaville flourished as kauri fell and mills buzzed. Immigrants from Britain and Croatia were attracted to the area. Ships up to 3,000 tons carried timber and logs out along the Wairoa to defy the bar at the harbour entrance before continuing on, usually to another New Zealand port or across the Tasman to Australia.[24]

The Kaipara River is the principal river feeding Kaipara Harbour from the south. From 1863 Helensville established itself as a timber port on this river, and provided shipping services about the Kaipara. When the timber ran out, Helensville developed sheep and dairy farms, and more recently nut plantations, vineyards and deer farms.[23]

Further south, Riverhead was an important trading link with the Kaipara and Helensville, and a centre for gum digging. Also set by a river, it milled timber and flour, and made paper. Later it turned to tobacco. From 1929 to 1933, the Riverhead State Forest was developed from 5,000 ha of exhausted gum land.[23]

As the kauri ran out, the Kaipara became a backwater.[23] After 1920 the gum and timber industries dwindled, and farming, mainly dairying, took over. In particular, there is dairying on the rich Ruāwai flats. These flats are below sea level, and are protected by a stopbank and a drainage system.[24] Coastal sawmill settlements at Tinopai, Arapaoa, Batley, Matakohe, Oneriri, Ōruawharo, Pahi, Paparoa, Tanoa and Whakapirau have become quiet backwaters. Pahi has become a launch point for houseboats and fishing. Matakohe has a museum which commemorates the kauri industry and the early Pākehā settlers.[21]

Today, Dargaville is the principle centre in the Kaipara area. Its population levelled in the 1960s. It is the country’s main kūmara (sweet potato) producer.[24]

In 2009, NIWA scientists discovered that 98 percent of snapper on the west coast of the North Island were originally juveniles from nurseries in the Kaipara. Snapper is New Zealand’s largest recreational fishery, and is also a commercial fishery with an annual export value of $32 million. The findings show how fragile some fish stocks can be, and highlights the importance of protecting natural habitats, like the Kaipara.

The scallop population has periodic incidences of high mortality, the causes of which have not been identified. Concerns in recent years about the size and availability of scallops have resulted in temporary closures of the scallop fisheries.[26][27]

Early versions of oyster farming occurred between the early 1900s and 1950s. Thousands of tons of rocks were placed along the shorelines to act as an additional substrate on which the natural rock oyster could grow.[15][28] In 2002, the Crown settled the historical claims of Te Uri o Hau, a hapu of the northern Kaipara Harbour. As part of the settlement, access to and the rights of the hapu to gather oysters within the existing "Maori Oyster Areas" were recognised.[29][30] In 2008, resource consent was given to Biomarine to establish New Zealand’s largest oyster farm in the Kaipara. The farm is projected to produce about NZ$30 million in annual exports and 100 new jobs.[31]

In recent years, there has been a perception amongst locals that commercial fishers have damaged fisheries in the Kaipara. Locals have been frustrated in their attempts to gain government support. The veteran filmmaker Barry Barclay has examined this in his 2005 documentary, The Kaipara affair.[21][32][33]

Currently (2007) about 219,000 cubic metres of sand is mined each year from the entrance and tidal deltas of the Kaipara. This sand contributes over half the sand requirements for Auckland. The sand is used in the production of concrete and asphalt, and also in drainage systems and beach nourishment. A suction pump is usually used to extract the sand from the seabed. It is pumped into a barge as a sand and water slurry. As the barge loads, shells and other objects are screened out and the sea water drained back to the sea. The availability of sea sand within the Auckland region means the road costs of transporting sand from further parts of the country are avoided.[34] Concerns about possible negative consequences of this sand mining have also been raised.[35][36]

In 2008, Crest Energy, a power company, received resource consent to install about 200 underwater tidal turbines in the Kaipara Harbour, which would use the substantial tidal flows moving in and out every day near the harbour mouth to produce electricity for approximately 250,000 homes.[38]

Crest plans to place the turbines at least 30 metres deep along a ten kilometre stretch of the main channel. Historical charts show this stretch of the channel has changed little over 150 years. The output of the turbines will cycle twice daily with the predictable rise and fall of the tide. Each turbine will have a maximum output of 1.2 MW, and is expected to generate 0.75 MW averaged over time.[9][39]

The peak level of generation for the combined turbines is about 200 MW. This exceeds the projected peak electricity needs of Northland. It would have environmental benefits in offsetting annual carbon emissions from a thermal-based, gas turbine generator of 575,000 tonnes of carbon.[9] The project is costed at about $600 million and to be economic would have to be scaled up rapidly to near full capacity.[40]

However, while the Department of Conservation has approved the project, and has made substantial environmental monitoring conditions part of the consent, the project also has objectors on the grounds of claimed influences on the local ecosystems and charter fishing (see the section above on fisheries). Appeals before the Environment Court are still likely.[41]

The Ministry of Fishing allocates quota for the north west region of New Zealand as a whole, but does not tailor quota specifically for the Kaipara. Local iwi feel they are not sufficiently involved in management issues, and to further compound matters, the local iwi is split between Te Uri-o-Hau in the northern part and Te Taoū in the southern part.[citation needed]

Ecological management and environmental issues are discussed in the Ecology section.

As of 2011, the environmental state of the harbour has been called as "nearing crisis" and "in significant decline", with shrinking fish and shellfish stocks, more sedimentation, declining water quality and competition for resource use and development being noted as the main issues, with "ninety-nine per cent of the rivers in the catchment [are] polluted".[7]

As part of the worldwide trend, there is a decline in biodiversity within the Kaipara.[42] The timber industry removed most of the native forest. Much of the kauri and kahikatea forest, and scrub and riparian vegetation, has been replaced with farm and urban areas. Mangrove forests and wetlands have been "reclaimed". Soil erosion has increased on the land and sedimentation in the harbour. Shellfish abundance has declined, especially toheroa, scallops, tuatua, cockles and pipi. Finfish like mullet, snapper, kanae and school shark have diminished.[42]

Habitat fragmentation has also occurred. Natural vegetation in the Kaipara catchments have been reduced to islands of wetlands and forest in man-made landscapes—separated by urban areas, roads, exotic forests and pastures. More information is needed on biodiversity in the Kaipara Harbour and habitats in associated coastal areas. A recent pilot survey found that habitats in the estuaries are still extensive, but ninety percent of land cover is no longer indigenous wetland or vegetation. Even if the key existing areas were to be protected, further buffers and corridors that give better connection between the natural areas would be needed to encourage the recovery of biodiversity.[42]